Yes, to get teaching experience you will leave your MPI position for one term to teach some courses and replace a vacant professor position. Then the hiring commmission, who has already spotted you before and has encouraged you to apply for the open job is happy.

So bottom line: Your six years slavery as a postdoc/ non-tenure track admin teaching personnel is good for the German university system, but definately not for you.

Btw, it can happen that you won't get the job even you spent 5 decent years at MPI, because they finally will hire a student directly from the American market, who just got a top 5 with his advisor and the commission thinks he has more potential for the job than you. (and you can always gain teaching experience on the job: original quote from a member of the hiring commission)

The German postdoc/ pseudo-tenure track reality looks like this
In the best case:
you teach your 4-6 hours, can fill your teaching at least partly with "reading" seminars for students and you have lectures, seminars, Übungen with 20-30 students and hardly any adminstrative tasks to do.
In the worst case:
you teach more than this amount of time, because the senior faculty thinks it would be good to offer this or that extra course, they load you with introductionary courses with 200-300 students, you must create new courses from the skretch, and the head of th department thinks "es gehört zum guten Ton" that you sit in various meaningless commissions.
The reality is probably a linear combination of these two cases
Now. Do you get a reward for this work when submitting your CV for a senior job in Germany? The answer is NO.
All they look at is how well you published over the last 6 years, then they compare it with a postdoc from an MPI who did not teach one course and are surprised that you did not produce the same output.

typically 6-8 hours in total over two terms. In average about 3-4 hours per term. However terms are shorter than in Germany.
Less administration, but also obligations to take care of loads of ba- and ma-thesis.

The catch is what is your chance of gettting tenure:

UK in general very high (but permanent not tenured, tenure does not exist)
Bocconi: depends on the department, econ department very very difficult
Spain top schools, good chance to become permanent but very complicated to become civil servant (real tenured)

Given the discussion I am really wondering what you think the alternative is.
Could someone please eleborate on the teaching deals in places like Bocconi, LSE, Pompeau Fabra, Stockholm?
With regard to job market: at least at smaller German places I am familar with, no teaching experience and in particular no willingness to teach a lot is a deal breaker.

teaching deals abroad (tenure track):
typically 6-8 hours in total over two terms. In average about 3-4 hours per term. However terms are shorter than in Germany.
Less administration, but also obligations to take care of loads of ba- and ma-thesis.
The catch is what is your chance of gettting tenure:
UK in general very high (but permanent not tenured, tenure does not exist)
Bocconi: depends on the department, econ department very very difficult
Spain top schools, good chance to become permanent but very complicated to become civil servant (real tenured)

Given the discussion I am really wondering what you think the alternative is.
Could someone please eleborate on the teaching deals in places like Bocconi, LSE, Pompeau Fabra, Stockholm?
With regard to job market: at least at smaller German places I am familar with, no teaching experience and in particular no willingness to teach a lot is a deal breaker.

Could smb please elaborate on what "negotiations" mean?? What is it about?

When you get an offer for a W3 (z to a limited extend for W-2) you negotiate bonus payments above your base pay, resources for research, Mitarbeiterstellen including secretary time, starting money for equipment, often rooms and even parking space or other extras.